Polyarylene sulfide (hereinafter, also referred to as “PAS”), represented by polyphenylene sulfide (hereinafter, also referred to as “PPS”), is an engineering plastic having excellent heat resistance, chemical resistance, flame retardancy, mechanical strength, electrical characteristics, dimensional stability, and the like. PAS can be formed into various molded products, films, sheets, fibers, and the like by ordinary melt processing methods such as extrusion molding, injection molding, and compression molding. Therefore, PAS has been widely used in a wide variety of fields, such as electric devices, electronic devices, devices for automobiles, and packaging material.
In the production of PAS, water mixed into the reaction system together with the starting materials, and water produced by the reaction are likely to induce side reactions at the time of polymerization, and inhibit the macromolecularization of PAS. Therefore, a method of polymerizing PAS while minimizing the water content present in the reaction system has been proposed. For example, there is a known method of performing polymerization while reducing the water content present in the reaction system to or below a certain level by performing dehydration from a water-containing sulfur source and performing dehydration by further removing water (for example, Patent Document 1).